Motors Book - Chapter 2

A nameplate is a metal tag permanently attached to an electric motor frame that provides important information about the motor, such as its electrical ratings, operating rating, and mechanical-design codes. This information is crucial for ensuring that the motor is used correctly and safely. The nameplate serves as a reference guide for technicians and engineers who need to know the specifications of the motor for maintenance, repairs, or replacements. It is an essential component of the motor that helps in identifying and understanding its capabilities and limitations.

The electrical ratings included on motor nameplates include a current rating, frequency rating, and voltage rating. These ratings provide important information about the motor's operating characteristics. The current rating indicates the amount of electrical current the motor requires to function properly. The frequency rating specifies the frequency of the electrical power supply that the motor is designed to operate on. The voltage rating indicates the voltage level at which the motor should be operated. Therefore, all of the given options - current, frequency, and voltage - are included in the electrical ratings on motor nameplates.

An enclosure is the type of protection given to a motor to shield it from the outside environment as well as to protect individuals from the electrical and rotating parts of the motor. The enclosure acts as a barrier, preventing dust, moisture, and other contaminants from entering the motor and potentially causing damage or malfunction. It also serves as a safety measure, preventing accidental contact with the electrical and rotating parts of the motor, reducing the risk of injury.

A motor bearing is a machine component that is used to reduce friction and maintain clearance between stationary and moving parts in a motor. It helps to support and guide the rotating shaft of the motor, allowing it to spin smoothly and efficiently. Without a motor bearing, there would be excessive friction and wear between the moving parts, leading to decreased performance and potential damage to the motor.

Locked-rotor current refers to the amount of current that a motor draws when the rotor is locked or unable to rotate. This typically occurs during motor startup or when there is a mechanical fault causing the rotor to be stuck. The locked-rotor current is usually higher than the normal operating current and is important to consider for motor sizing and protection.

The current rating is the amount of current a motor draws when delivering full rated power output. This indicates the maximum amount of electric current that the motor can handle without overheating or causing damage. It is important to ensure that the motor's current rating matches the electrical system it is connected to in order to prevent any potential issues or failures.

The insulation class is a code letter that indicates the maximum operating temperature of the insulation in a motor. This is important because the insulation must be able to withstand the heat generated during operation to prevent damage to the motor. Different insulation classes are assigned different temperature limits, allowing motor manufacturers and users to select the appropriate insulation class based on the specific requirements of the application.

Intermittent-rated motors are used in applications where the motor only needs to be turned on for short time periods to meet the application requirements. These motors are designed to handle the intermittent nature of the workload and are not meant for continuous operation. They are commonly used in applications such as compressors, waste-disposal systems, electric hoists, gate opening motors, and other similar applications.

The rating that describes the expected or allowed application of a motor is known as the usage rating. This rating provides information about the specific purposes or applications for which the motor is designed and can be safely used. It helps users determine whether a particular motor is suitable for their intended purposes and ensures that the motor is used within its specified capabilities.

The NEMA design letter is a code letter that represents the National Electrical Manufacturers Association (NEMA) motor classification for the torque and current curves of a motor. This letter indicates the motor's ability to withstand certain operating conditions and provides information about its performance characteristics. It is used to classify motors based on their design features and is an important factor in selecting the right motor for a specific application.

The operating time rating refers to the amount of time a motor can be continuously operated without being turned off in order to allow for cooling. This rating is important as motors generate heat during operation, and continuous running without adequate cooling can lead to overheating and potential damage to the motor. Therefore, the operating time rating provides a guideline for the maximum duration that the motor can be operated before it needs to be turned off to prevent overheating.

The given statement mentions different types of motor enclosures, such as general, dripproof, splashproof, guarded, semiguarded, and dripproof fully guarded. However, "open" is not mentioned as one of the types. Therefore, the correct answer is "open" because it is not included in the list of motor enclosure types provided.

Design L motor is an integral-horsepower single-phase motor design made for full-voltage starting and locked-rotor torque higher than for design M, N, and O motor.

The permissible temperature rating refers to the maximum temperature difference allowed between the winding temperature of a running motor and the ambient temperature. It indicates the limit within which the motor can safely operate without overheating. This rating is crucial for ensuring the motor's longevity and preventing any damage or malfunction caused by excessive heat.

The correct answer is E. The design E motor is specifically designed for full-voltage starting and high locked-rotor torque, while also ensuring that the locked-rotor current does not exceed a specified value.